This invention generally relates to catheters, and particularly intravascular catheters for use in percutaneous transluminal coronary angioplasty (PTCA) or for the delivery of stents.
In percutaneous transluminal coronary angioplasty (PTCA) procedures a guiding catheter is advanced in the patient's vasculature until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. A dilatation catheter, having an inflatable balloon on the distal portion thereof, is advanced into the patient's coronary anatomy over the previously introduced guidewire until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with inflation fluid one or more times to a predetermined size at relatively high pressures so that the stenosis is compressed against the arterial wall and the wall expanded to open up the vascular passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter and the guidewire can be removed therefrom.
In such angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate of angioplasty alone and to strengthen the dilated area, physicians may implant an intravascular prosthesis, generally called a stent, inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel or to maintain its patency. A tubular cover formed of synthetic or natural material may be present on an outer or inner surface of the stent. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded within the patient's artery to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. See for example, U.S. Pat. No. 5,507,768 (Lau et al.) and U.S. Pat. No. 5,458,615 (Klemm et al.), which are incorporated herein by reference.
In the design of catheter balloons, characteristics such as strength, compliance, and profile of the balloon are carefully tailored depending on the desired use of the balloon catheter, and the balloon material and manufacturing procedure are chosen to provide the desired balloon characteristics. A variety of polymeric materials are conventionally used in catheter balloons. Use of polymeric materials such as PET that do not stretch appreciably consequently necessitates that the balloon is formed by blow molding, and the deflated balloon material is folded around the catheter shaft in the form of wings, prior to inflation in the patient's body lumen. However, it can be desirable to employ balloons, referred to as formed in place balloons, that are not folded prior to inflation, but which are instead expanded to the working diameter within the patient's body lumen from a generally cylindrical or tubular shape (i.e., essentially no wings) that conforms to the catheter shaft.
Catheter balloons formed of expanded polytetrafluoroethylene (ePTFE) expanded in place within the patient's body lumen provide an alternative to folded balloons. ePTFE is PTFE that has been expanded, and ePTFE typically has a microporous structure comprising nodes interconnected by fibrils.
Since compliant polymers such as ePTFE may be a porous material it is typically combined with a nonporous liner as part of the balloon's construction. The material used to form the liner may consist of a separate layer that neither fills the pores nor disturbs the node and fibril structure of the ePTFE or other polymeric layer, or it may at least partially fill the pores of the porous layer. The nonporous or low porosity liner is typically an elastomeric material that limits or prevents leakage of the inflation fluid through the microporous balloon layer when the balloon is inflated through pressurization via an inflation lumen. Another function of the nonporous liner is in deflating, i.e., restoring, the balloon to a low profile after inflation. The liner expands elastically during inflation of the balloon but has a shape memory such that, upon depressurization, the liner retracts the inflated polymeric layer back to a low profile configuration that promotes a safer withdrawal of the balloon catheter.
One difficulty has been providing an ePTFE balloon with sufficiently high rupture pressure. Some liner bonding techniques such as laser bonding the liner tubing to the outer surfaces of the catheter shaft results in wall thinning of the tubular liner in proximity with the bonding area. This reduction in wall thickness of the liner can be uneven and result in thin spots or weakened areas that place the integrity of the balloon at risk. Upon inflation of the balloon to elevated pressures of eight atmospheres or higher, these weaknesses due to the liner thinning at the bonding surfaces may lead to early rupture of the balloon. Stress concentrations are particularly elevated at the distal end of the balloon, where the inflection point of the tapered distal end portion and the bonded portion occurs.